DARWIN 129 



Deity quite so naively as Agassiz in zoology and 

 botany, conceived a "law of development " within 

 life itself. It was a time when belief in a "vital 

 force " was universal. Living things had their 

 peculiar force, which was not found in lifeless 

 things. The life-principle might be at work in the 

 law of development. It would raise living things 

 higher and higher in the succeeding geological 

 epochs. It was a vague theory, though it purported 

 to cover not only the fact but the machinery of 

 development. In the course of ages it brought 

 about the appearance of new species. Those who 

 held this idea of an immanent law of evolution 

 rejected the older notion of a personal Deity, 

 putting in an appearance suddenly at thejbeginning 

 of the secondary period and creating the ichthyo- 

 sauri " out of nothing." They looked upon 

 Cuvier's catastrophes, to which Agassiz still clung, 

 with a touch of Lyell's scepticism. The "law 

 of evolution" had been the deus ex machina of 

 the long procession of life-forms. One day a fish 

 ceased to give birth to little fishes in the manner 

 of its parents. The "law of evolution" was at 

 work in its ova, and suddenly little ichthyosauri 

 were developed from them. Thus, again, a lizard 

 was believed to have engendered young mammals 

 one day. One student would hold that the tran- 

 sition was quite abrupt in this sense. Another 

 would think it more gradual, and approach the 

 idea of a slow transformation of a fish into a 

 lizard, and a lizard into a mammal, or a tree-fern 

 into a palm-fern, and this into a true palm. At 



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